(1) Field of the Invention
The present invention relates to telephone system ringing systems and more particularly to a ringing signal generator capable of a plurality of ringing telephone substations each responsive to at least one of a plurality of different ringing signal frequencies.
(2) Description of the Prior Art
Some telephone system stations often include telephones which respond to different ringing frequencies. Therefore, in order to ring a selected telephone, the control system must apply a ringing signal of a frequency to which the particular telephone will respond.
Various methods have been employed to ring tuned ringers of different frequencies from one ringing supply. One approach is to use selective strapping arrangements to connect the ringing signal of the required frequency only to those telephone substations tuned to that particular frequency. A more modern approach is to use a data base that determines the ringing frequency necessary for each subscriber. This method involves storing the subscriber ringing frequency data, recalling it every time the subscriber's telephone is to be rung, and programming a programmable ringing generator. This data frequently must be changed when changes in the substation telephone are made.
These prior art methods incur substantial penalties in the form of cost, size and/or limitations on performance.
Accordingly it is an object of the present invention to provide a novel, low cost, reliable technique of ringing tuned ringers.